The use of pliers to grip, twist, and cut wires has long assisted workers and tradesmen in performing their duties quickly and effectively. Originally, pliers were in the form of single purpose tools which could perform only a single function e.g., gripping exclusively. Thus, a tradesman was required to have a different pair of pliers for each task.
As the nature of equipment and tools became more sophisticated, the use of single function pliers became disadvantageous due the large variety and types of pliers required to perform a particular task. Eventually, multi-functional pliers were developed that would perform the same functions as would several single function pliers. In this manner, the tradesman saved money and time by having to purchase only one pair of pliers that could perform several functions.
A common, but critical, practice that requires the use of multi-functional pliers is the locking of screws or bolts on machinery that is subject to considerable vibrations, such as on engines for aircraft and the like. By providing a hole through a head of a bolt, a wire may be inserted through the hole and then secured or anchored to another object to prevent the bolt from unfastening when subjected to high levels of vibration.
In particular, one end of a high tensile steel wire would be passed through the hole in the head of a bolt and drawn through to a particular length. The wire would then be drawn for a length greater than the distance between the next adjacent bolt desired to be wire locked or an anchoring object. The wire is then pulled tight and twisted in order to maintain the wire taut. In a similar fashion, one of the ends of the wire would then be passed through the hole of the adjacent bolt or anchoring object and then drawn tight and twisted up to a distance approximately equal to the next adjacent bolt or anchor object. After the final bolt or anchoring object is locked, the wire must be tied at the ends and any excess wire remaining must be cut. The wire is then bent over so that it is out of the way. A wire is typically long enough to allow locking of two or three bolts, but other lengths are possible and one may also wire lock a single bolt.
Plier designers have had limited success in designing a pair of pliers that perform the gripping, twisting, and cutting functions that are essential to wire locking without nicking or scraping the wire. Flat, smooth jaw surfaces did not impart sufficient friction to keep wires from pulling out of the jaws. Hence, some designers have provided pliers with serrated wire gripping surfaces which provide a secure grip of the wire during the gripping and twisting phases of the wire locking process. However, the serrated gripping surfaces function primarily by cutting into the wire, thereby creating portions of wire which contained nicks and scrapes. These nicks and scrapes made the wire increasingly susceptible to failure at those portions, thereby limiting the amount of tension that the wires may withstand.
To solve these problems, designers developed pliers that incorporated wavy or undulating gripping surfaces that were not serrated. These undulations provided a slope that increased the frictional resistance on the wire and the lack of serrations or sharp corners eliminated nicking and scraping of the wire. However, the previous designs suffered from several disadvantages: 1) the large amplitudes necessary to increase the frictional resistance are too great to allow formed wire to pass through standard pre-drilled holes, and 2) the sine wave pattern exhibiting equivalent radii does not permit the jaw gripping force to be fully distributed along the wire. Resultingly, these designs served to pinch or flatten the wire at the slope transition which caused an unacceptable deformation.
Also, since wire locking is often performed in sensitive environments, such as engine bays, the tradesman had to ensure that the excess wire cut off did not fall into the engine. When the wires were cut, the force applied by the pliers tended to produce a force perpendicular to the cut, which in effect, "shot" the loose end of the wire away from the pliers. A piece of wire unaccounted for in such a sensitive environment could have disastrous effects and thus must be located at all costs.
To solve this problem, plier designers provided a resilient material between the plier's jaws to hold the loose end during cutting thereby preventing it from falling into unwanted areas. However, through normal usage the resilient material eventually detached itself from the pliers. The pliers then had to be discarded and replaced with a new pair.